problem with back up lights

[dyingdeadman]

i have a problem with my back up lights. they seem to stay on when the headlihts or parking lights are on. weird thing is they dont do it all the time just sometimes after reversing they wont go off, then a little while later they will shut off and not come back on untill i put it in reverse again,but then they will just stay on after putting in drive. i think there must be a short somewhere, but not sure where to start.